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BUG: KCSAN: data-race in bio_endio / blk_update_request

read to 0xffff88809c3d0494 of 2 bytes by interrupt on cpu 1:
 bio_remaining_done block/bio.c:1760 [inline]
 bio_endio+0x3e/0x400 block/bio.c:1790
 req_bio_endio block/blk-core.c:245 [inline]
 blk_update_request+0x427/0x7b0 block/blk-core.c:1464
 blk_mq_end_request+0x3f/0x2b0 block/blk-mq.c:546
 end_cmd drivers/block/null_blk_main.c:648 [inline]
 end_cmd+0xa9/0x1a0 drivers/block/null_blk_main.c:642
 null_complete_rq+0x22/0x30 drivers/block/null_blk_main.c:675
 blk_done_softirq+0x1eb/0x250 block/blk-softirq.c:37
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 run_ksoftirqd+0x46/0x60 kernel/softirq.c:603
 smpboot_thread_fn+0x37d/0x4a0 kernel/smpboot.c:165
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

write to 0xffff88809c3d0494 of 2 bytes by interrupt on cpu 0:
 bio_clear_flag include/linux/bio.h:244 [inline]
 blk_update_request+0x36a/0x7b0 block/blk-core.c:1463
 blk_mq_end_request+0x3f/0x2b0 block/blk-mq.c:546
 end_cmd drivers/block/null_blk_main.c:648 [inline]
 end_cmd+0xa9/0x1a0 drivers/block/null_blk_main.c:642
 null_complete_rq+0x22/0x30 drivers/block/null_blk_main.c:675
 blk_done_softirq+0x1eb/0x250 block/blk-softirq.c:37
 __do_softirq+0x115/0x33f kernel/softirq.c:292
 run_ksoftirqd+0x46/0x60 kernel/softirq.c:603
 smpboot_thread_fn+0x37d/0x4a0 kernel/smpboot.c:165
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9 Comm: ksoftirqd/0 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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